Time-resolved photoacoustic calorimetry is a technique developed in our laboratory that enables one to determine both the dynamics and reaction enthalpy for photoinitiated reactions that generate either stable products or transient intermediates. The capabilities of the technique are such thjat the sum of the reaction enthalpies for reactions on the timescale of 10 nanoseconds or less can be directly measured. For reaction times ranging from 40 nanosecond to 50 microseconds both the dynamics and reaction enthalpy can be determined. For reactions in aqueous media, it is possible to measure the dynamics and amplitudes of volume changes associated with the reactions on the timescale of 40 nanosecond to 50 microseconds. We propose to examine the chemistry of myoglobin and hemoglobin that results from the photolysis of carboxymyoglobin and carboxyhemoglobin. For each intermediate in the 40 nanosecond to 50 microsecond time domain, the dynamics and amplitude of the enthalpy and volume changes associated with the decay of each intermediate will be measured. The values obtained from the enthalpy and volume changes resulting from time-resolved photoacoustic calorimetry will be important new data for the development of models for protein dynamics and the development of a molecular model for the cooperative binding of ligands to hemoglobin.